Shadow mask for a color television image tube

ABSTRACT

An improved shadow mask for a color television image tube is shown to comprise a thin metal sheet having a translucent area defined by a multiplicity of dot-like apertures extending through the sheet, the sheet being formed of a composite metal laminate having at least one layer of steel providing the shadow mask with desired strength and having at least one layer of another metal such as copper of relatively greater thermal conductivity for conducting heat rapidly away from parts of the translucent mask area which become locally overheated during image tube operation, thereby to avoid local deformations of the translucent mask area such as would cause distortion or blurring of the image produced by the tube.

Savolainen et al.

[ SHADOW MASK FOR A COLOR TELEVISION IMAGE TUBE [75] Inventors: Unto U. Savolainen; Henry Ty. both of Attleboro, Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas. Tex.

[22] Filed: Dec. 13, 1972 [21] Appl. No: 314,872

[52] US. Cl. 29/1835; 29/1963; 29/l9l.4; 29/180; 29/1966 [51] Int. Cl 823p 15/16 [58] Field of Search 29/1963. 195.5,191, 183.5, 29/1914 [56] References Cited UNITED STATES PATENTS 3212.865 10/1965 Miller 29/l96.3 X

[451 May 13,1975

Primary E.raminerl-lelen M. McCarthy Assistant Examiner-O. F. Crutchfield Attorney, Agent, or Firm-James P. McAndrews; John A. Haug; Edward J. Connors, Jr.

[57] ABSTRACT An improved shadow mask for a color television image tube is shown to comprise a thin metal sheet having a translucent area defined by a multiplicity of dot-like apertures extending through the sheet. the sheet being formed of a composite metal laminate having at least one layer of steel providing the shadow mask with desired strength and having at least one layer of another metal such as copper of relatively greater thermal conductivity for conducting heat rapidly away from parts of the translucent mask area which become locally overheated during image tube operation, thereby to avoid local deformations of the translucent mask area such as would cause distortion or blurring of the image produced by the tube.

17 Claims, 6 Drawing Figures SHADOW MASK FOR A COLOR TELEVISION IMAGE TUBE In conventional color television image tubes. light emitting phosphors of different types are arranged in groups on the inside of the front face of the image tube envelope so that electrons emitted from sources within the tube are guided by tube deflection means to im pingc upon selected phosphors for forming a light image on the tube face. Customarily. a thin shcet-likc shadow mask is disposed within the image tube between the electron sources and the tube face. this mask having a translucent area defined by a multiplicity of apertures which extend through the mask. As will be understood. the mask is positioned within the tube so that electrons guided along selected paths pass through selected mask apertures to impinge upon selected phosphors for producing the desired light image whereas other electrons are intercepted by the mask so that these electrons cannot blur. distort or otherwise degrade the light image. In conventional color television image tubes. thermostat metal mounting means adjustably support the shadow mask and. as the mask and other tube components are subjected to thermal expansion when the tube is heating up after initiation of tube operation. the thermostat metal mounting means move the mask to compensate for such thermal expansion and to retain the desired alignment of the mask apertures with respective light-emitting phosphors.

It has now been found that. although the thermostat metal mounting of the shadow mask adequately compensates for overall thermal expansion of the shadow mask after tube operation is initiated. the translucent areas of the shadow mask tend to be subject to localized overheating throughout the period of tube operation. For example. when the image produced by the tube remains substantially the same for a significant period of time. electrons tend to be passed through the same mask apertures or to be intercepted by the same portions of the mask for a considerable period of time. Thus, the mask portions intercepting the electrons tend to become heated to a higher temperature than adjacent mask portions. The temperature differentials thus established across the translucent area of the mask causes local deformations of the mask with the result that mask apertures in selected portions of the mask become misaligned with respect to the light-emitting phosphors on the tube face and cause distortion of part of the light image formed by the tube.

It is an object of this invention to provide a novel and improved shadow mask for a color television image tube; to provide such an improved shadow mask which is significantly less subject to localized deformations of the mask during image tube operation; and to provide such an improved shadow mask which is of strong but economical construction Other objects. advantages and details of the novel and improved shadow mask construction provided by this invention appear in the following detailed description of preferred embodiments of this invention. the detailed description referring to the drawings in which:

FIG. I is a plan elevation view. partially cut away. of a color television image tube incorporating the improved shadow mask of this invention;

H6. 2 is a section view along line 22 of FlG. 1'.

FIG. 3 is a section view along line 33 of FIG. 2;

H6. 4 is a partial perspective view of the shadow mask construction of the prior art;

HO. 5 is a partial section view similar to FIG. 3 illustrating an alternate embodiment of this invention; and

HO. 6 is a partial section view similar to FIG. 3 illustrating another alternate embodiment of this invention.

Referring to the drawings. 10 in FIGS. l-3 indicates the novel and improved shadow mask of this invention which is shown incorporated within a color television image tube 12. The shadow mask 10 of this invention is conventional with respect to its general configuration in that the mask includes a thin sheet-like portion [4 and suitable flange means 16 and in that a translucent area 18(see H6. 2) of the mask is defined by a multiplicity of dot-like apertures 20 which are arranged in a pattern to extend through the sheet-like portion 14 of the mask. That is. the area of the mask 10 is referred to as translucent herein because. although the sheet material ofthe mask is opaque, a large number ofapcrtures 20 define the area 18 and each aperture is adapted to transmit electrons as well as light through the apertures. The flange means [6 of the shadow mask is preferably integral with the sheet-like portion [4 of the mask is illustrated to provide the unimask type of construction wherein the integral flange extends at approximately a right angle to the general plane of the sheet portion of the mask entirely around the periphery of the mask. However. any other conventional flange means for use in mounting the mask 10 are also within the scope of this invention. Preferably. also. the sheetlike portion 14 of the shadow mask 10 has a small, general concavity as is best illustrated in FIGS. 1 and 3.

The shadow mask 10 is also adapted to be mounted on a color television image tube 12 in a conventional manner. That is. as shown in the drawings. the image tube 12 typically includes a tube envelope 22 having a front face 24 and has a multiplicity of light-emitting phosphors of three different types arranged in groups on the inside of the front face of the tube envelope as is generally indicated at 26. The image tube also includes electron source means as diagrammatically illustrated at 28 in FIG. 1 and has pins 30 integrally formed as part of the tube envelope. Any conventional thermostat metal mounting means 32 are then secured to the flange 16 of the shadow mask and attached at one end to respective mounting pins 30 on the tube envelope for mounting the shadow mask 10 in any conventional manner within the tube between the electron source means 28 and the light-emitting phosphors 26 on the tube face 24 for automatically adjusting the position of the shadow mask in conventional manner as the overall temperature of the mask increases after initiation of image tube operation. As the color television image tube 12 and the general configuration and mounting of the shadow mask 10 are conventional. they are not further described herein and it will be understood that the mask 10 is adapted to permit properly directed elec trons emitted from the source means 28 to pass through selected apertures 20 in the mask to impinge upon selectcd phosphors 26 to form a light image on the tube face 24 but is adapted to intercept other electrons emitted by the source means before such other electrons can impinge on the phosphors 26, thereby to keep these other electrons from distorting or blurring the light image formed by the image tube [2.

In accordance with this invention. at least the thin sheet-like portion of the shadow mask 10. and preferably the entire shadow mask 10 particularly where the mask is of the unimask construction. is formed of a composite metal laminate material having a plurality of layers of metal metallurgically bonded together as shown in FlG. 3. Preferably. the shadow mask 10 embodies two layers of mild steel 34 having a layer of copper 36 or other metal material of relatively greater thermal conductivity than the material of layers 34 sandwiched between and mctallurgically bonded to the metal layers 34 substantially throughout the interfaces 38 between the metal layers. Typically. for example. each of the metal layers 34 has a thickness of about 0.0018 inches and is formed of SAE 10 I Low Carbon Steel having a composition. by weight. of 0.08 to 0.13 percent carbon. 0.30 to 0.60 percent manganese. 0.040 percent max.) phosphorous. 0.050 percent max.) silicon. and the balance iron. The copper layer 36 of the composite material is then desirably provided with a thickness of about 0.0024 inches and is formed of any conventional copper sheet material such as electrolytic tough pitch copper or the like. As will be understood, such layer materials are readily formed into the desired composite metal laminate by conventional roll bonding techniques and preferably. the composite material is annealed after such roll-bonding.

It will be understood, that the steel layers ofthe composite can be formed of other conventional mild or stainless steels or the like within the scope of this invention and that the steel layer can vary in thickness from about 0.00l to 0.004 inches while the copper layer thickness can vary from about 0.00l to about 0.008 inches within the scope of this invention.

The advantages of the shadow mask of this inven tion are best described by reference to FIG. 4 which illustrates the conventional shadow mask 40 of the prior art having a thin sheet-like portion 42 and having a multiplicity of dot-like apertures 44 extending through this sheet-like mask portion to define a translucent mask area 46. As illustrated. when a portion 48 of the conventional mask tends to intercept electrons for any significant period of time while other portions of the mask 40 are intercepting electrons with lesser fre quency. the identified mask portion 48 tends to become heated to a relatively higher temperature than adjacent mask portions so that, even when the translucent area of the mask is provided with a small general concavity as shown in FIG. 4, the mask portion 48 tends to be bulged or bubbled out as shown in FIG. 4 to create a local deformation in the translucent mask area. As will be understood. this local mask deformation causes some misalignment of the mask apertures with selected light-emitting phosphors on the tube face causing some blurring and distortion of the image produced by the conventional image tube.

With the shadow mask 10 of this invention, however. the steel layers 34 of the mask provide the mask with suitable strength. These steel layers are also adapted to be easily darkened to facilitate heat radiation from the mask. The copper layer 36 of the improved shadow mask 10 then provides the mask with greatly improved effective thermal conductivity properties so that the mask is adapted to rapidly distribute absorbed heat throughout the mask for reducing or even effectively preventing any significant temperature differentials across the translucent area of the mask and for preventing any local deformation of translucent areas of the improved mask. The mild steel mask layer 34 closest to the image tube face 24 could be omitted within the scope of this invention if desired but is preferably employed as shown to contribute to mask strength. to make the composite laminate material symmetrical for convenience in shaping the material into shadow mask configuration. and. most important, for thermally balancing the composite material so that the composite material does not tend to flex or bend as a result of differences in coefficients of thermal expansion between the copper and steel materials of the composite. Most important. the copper layer of the improved shadow mask 10 also contributes significantly in making the shadow mask easier to manufacture, particularly where the shadow mask 10 is to be provided in the unimask type of configuration having integral flanges 16 as illus trated in FIGS. 1-3. That is. the presence ofthe copper core layer 36 makes the composite material much eas ier to deep-draw into the desired mask configuration and is frequently found to improve the elongation that can be obtained in the steel layers of the composite be fore an intermediate annealing step is required during the deep drawing. Further, when the apertures 20 are formed in the mask 10 in a two stage etching process in otherwise conventional manner one ctchant being used to etch the steel material and then a second etchant being used to etch apertures in the copper layer of the composite material the resulting apertures are usually found to display less total taper so that finer apertures are more easily provided in the improved shadow mask.

lf desired, as illustrated in FIG. 4, a very thin layer of nickel 50 is also desirably bonded to one side of the composite material embodied in the shadow mask 10 for further facilitating etching of the apertures 20 in the shadow mask. This nickel layer is desirably provided on the described composite material by roll-bonding as above-described or may be added to the roll-bonded steel-copper-steel composite previously described by electroplating or the like. As shown in H0. 5, an additional thin layer of nickel is also desirably bonded to the opposite of the steel-eopper-steel material previously described for thermally balancing the composite material and to make the material symmetrical for greater convenience in manufacturing the shadow mask of this invention from the composite material. Preferably each such layer of nickel has a thickness in the range from about 0.000] to about 0.001 inches, the thinner dimensions being used where the nickel layer is formed by electroplating and the thicker dimensions being preferred where the nickel layers are roll-bonded to the steel layers of the composite.

It should be understood that although particular embodiments of the shadow mask of this invention have been described by way of illustrating the invention, this invention includes all modifications and equivalents of the disclosed embodiments falling within the scope of the appended claims.

We claim:

1. An improved shadow mask for a color television image tube comprising a thin metal sheet having a translucent area defined by a multiplicity of dot-like apertures extending through said sheet. said thin metal sheet being ofa composite metal laminate material embodying at least one layer of mild steel material and embodying at least one layer of metal of relatively greater thermal conductivity than said mild steel mate rial for reducing the occurrence of local temperature differentials across said translucent mask area to prevent local therrnal distortion of said translucent mask area.

2. An improved shadow mask as set forth in claim wherein said composite metal laminate material comprises a layer of mild steel metallurgically bonded to a layer of copper.

3. An improved shadow mask as set forth in claim I wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two outer layers of mild steel.

4. An improved shadow mask as set forth in claim I wherein said composite metal laminate material comprises a layer of mild steel having a layer of copper metallurgically bonded to one side of said layer of mild steel and having a layer of nickel secured to an opposite side of said layer of mild steel.

5. An improved shadow mask as set forth in claim 1 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two layers of mild steel and having an outer layer of nickel metallurgically bonded to each of said mild steel layers.

6. An improved shadow mask as set forth in claim 3 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches and said layer of copper has a thickness in the range from about 0.001 to about 0.008 inches.

7. An improved shadow mask as set forth in claim 5 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches. wherein said layer of copper has a thickness in the range from about 0.00] to 0.008 inches. and wherein each of said layers of nickel has a thickness in the range from about 0.000] to about 0.002 inches.

8. An improved shadow mask for a color television image tube comprising a member having a thin sheet metal portion of concave configuration and having an integral flange portion. said sheet metal portion having a translucent area defined by a multiplicity of dot-like apertures extending through said sheet metal portion. said member being formed of a composite metal laminate material embodying at least one layer of mild steel material and embodying at least one layer of metal of relatively greater thermal conductivity than said mild steel material for reducing local overheating of said sheet metal portion of said member from preventing local thermal distortion of said translucent mask area.

9. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of mild steel metallurgically bonded to a layer of copper.

10. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two outer layers of mild steel.

1]. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of mild steel having a layer ofcopper metallurgically bonded to one side of said layer of mild steel and having a layer of nickel secured to an opposite side of said layer of mild steel.

12. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two layers of mild steel and having an outer layer of nickel metallurgically bonded to each of said mild steel layers.

13. An improved shadow mask as set forth in claim 10 wherein each of said mild steel layers has a thickness in the range from about 0.00] to 0.004 inches and said layer of copper has a thickness in the range from about 0.00l to about 0.008 inches.

14. As improved shadow mask as set forth in claim 12 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches. wherein said layer of copper has a thickness in the range from about 0.001 to 0.008 inches. and wherein each of said layers of nickel has a thickness in the range from about 0.000l to about 0.002 inches.

15. An improved shadow mask as set forth in claim 8 wherein said metal laminate material comprises a layer of mild steel metallurgically bonded to a layer of copper. said layer of mild steel being disposed on the inner surface of said concave configuration.

16. An improved shadow mask as set forth in claim 1 wherein at least said translucent area of said metal sheet has a concave configuration.

17. An improved shadow mask as set forth in claim 16 wherein said metal sheet comprises a layer of mild steel metallurgically bonded to a layer of copper. said layer of mild steel being disposed on the inner surface of said concave configuration. 

1. AN IMPROVED SHADOW MASK FOR A COLOR TELEVISION IMAGE TUBE COMPRISING A THIN METAL SHEET HAVING A TRANSLUCENT AREA DEFINED BY A MULTIPLICITY OF DOT-LIKE APERTURES EXTENDING THROUGH SAID SHEET, SAID THIN METAL SHEET BEING OF A COMPOSITE METAL LAMINATE MATERAL EMBODYING AT LEAST ONE LAYER OF MILD STEEL MATERIAL AND EMBODYING AT LEAST ONE LAYER OF METAL OF RELATIVELY GREATER THERMAL CONDUCTIVITY THAN SAID MILD STEEL MATERIAL FOR REDUCING THE OCCURRENCE OF LOCAL TEMPERATURE DIFFERENTIALS ACROSS SAID TRANSLUCENT MASK AREA TO PREVENT LOCAL THERMAL DISTORATION OF SAID TRANSLUCENT MASK AREA.
 2. An improved shadow mask as set forth in claim 1 wherein said composite metal laminate material comprises a layer of mild steel metallurgically bonded to a layer of copper.
 3. An improved shadow mask as set forth in claim 1 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two outer layers of mild steel.
 4. An improved shadow mask as set forth in claim 1 wherein said composite metal laminate material comprises a layer of mild steel having a layer of copper metallurgically bonded to one side of said layer of mild steel and having a layer of nickel secured to an opposite side of said layer of mild steel.
 5. An improved shadow mask as set forth in claim 1 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two layers of mild steel and having an outer layer of nickel metallurgically bonded to each of said mild steel layers.
 6. An improved shadow mask as set forth in claim 3 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches and said layer of copper has a thickness in the range from about 0.001 to about 0.008 inches.
 7. An improved shadow mask as set forth in claim 5 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches, wherein said layer of copper has a thickness in the range from about 0.001 to 0.008 inches, and wherein each of said layers of nickel has a thickness in the range from about 0.0001 to about 0.002 inches.
 8. An improved shadow mask for a color television image tube comprising a member having a thin sheet metal portion of concave configuration and having an integral flange portion, said sheet metal portion having a translucent area defined by a multiplicity of dot-like apertures extending through said sheet metal portion, said member being formed of a composite metal laminate material embodying at least one layer of mild steel material and embodying at least one layer of metal of relatively greater thermal conductivity than said mild steel material for reducing local overheating of said sheet metal portion of said member from preventing local thermal distortion of said translucent mask area.
 9. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of mild steel metallurgically bonded to a layer of copper.
 10. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two outer layers of mild steel.
 11. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of mild steel having a layer of copper metallurgically bonded to one side of said layer of mild steel and having a layer of nickel secured to an opposite side of said layer of mild steel.
 12. An improved shadow mask as set forth in claim 8 wherein said composite metal laminate material comprises a layer of copper sandwiched between and metallurgically bonded to two layers of mild steel and having an outer layer of nickel metallurgically bonded to each of said mild steel layers.
 13. An improved shadow mask as set forth in claim 10 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches and said layer of copper has a thickness in the range from about 0.001 to about 0.008 inches.
 14. As improved shadow mask as set forth in claim 12 wherein each of said mild steel layers has a thickness in the range from about 0.001 to 0.004 inches, wherein said layer of copper has a thickness in the range from about 0.001 to 0.008 inches, and wherein each of said layers of nickel has a thickness in the range from about 0.0001 to about 0.002 inches.
 15. An improved shadow mask as set forth in claim 8 wherein said metal laminate material comprises a layer of mild steel metallurgically bonded to a layer of copper, said layer of mild steel being disposed on the inner surface of said concave configuration.
 16. An improved shadow mask as set forth in claim 1 wherein at least said translucent area of said metal sheet has a concave configuration.
 17. An improved shadow mask as set forth in claim 16 wherein said metal sheet comprises a layer of mild steel metallurgically bondeD to a layer of copper, said layer of mild steel being disposed on the inner surface of said concave configuration. 